Occupational and Health Regulations require that landfill sites be covered after each day's operation to prevent fire and health hazards which can come from decomposing rubbish. Traditionally a heavy layer of clean earth about 30 cm deep, has been used to cover the layer of rubbish pushed onto the site during the day and to prevent spontaneous combustion, odors, vermin and danger to people and animals on the site.
However this traditional method is costly and time consuming since supplies of clean earth have to be retained on the site and then uniformly spread to the required depth at the end of each day. Accordingly a range of alternatives have been developed to minimise the cost of and time required for ADC.
Many of these alternatives have involved the development of clay and other mineral compositions which are spread over the layer of rubbish to form a potentially impermeable cap. However these materials also have to be stored on site or nearby and take considerable time and labor to spread over the site.
A popular alternative involves using a film of material such as polythene which is spread over the fill usually by a mobile dispensing machine. However such films have to be weighted down usually by a layer of earth which in the case of the apparatus taught in U.S. Pat. No. 6,558,079 is also deposited and rolled on the film by the machine. The resulting covering is expensive since it consumes large quantities of earth, energy and time each day and does not provide effective protection against flies, birds, vermin and fire.
Another alternative is a foam technology wherein a mobile machine dispenses dense foam to cover the layer of rubbish. However the foam can be washed away by rain and blown away by high winds and once again the method requires large quantities of material and energy. Accordingly there is a need for a cost effective ADC which does not consume costly materials and which can secure a landfill site to the standard required by the relevant regulations.
The only ADC we have found which does not consume materials is disclosed in WO0232594. This system consists of a plurality of freely mobile support members with a cable array secured to the support members to form a supporting framework. A covering membrane is attached to the supporting framework to form an enclosure over the landfill site.
Although this apparatus covers the site, the cable array is particularly cumbersome to store, erect and to cover with a membrane and it would take some time to tension the cable array as required and to restrain the walls of the enclosure at ground level. Further the membrane is prone to tearing and contamination especially at ground level. Also since it is not vented there is a probability of the build up of methane and other flammable gasses in the enclosure with the attendant risk of fire.